Geometry Problem.

$M$ is the midpoint of $\overline{PQ}$ and $N$ is the midpoint of $\overline{PR}$, and $O$ is the intersection of $\overline{QN}$ and $\overline{RM}$, as shown. If $\overline{QN}\perp\overline{PR}$, $QN = 12$ ,and $PR = 14$, then find $OR$ 

Please help, thanks.